Fluid flow and heat transfer in wavy microchannels Y. Sui, C.J. Teo * , P.S. Lee, Y.T. Chew, C. Shu Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore article info Article history: Received 21 August 2009 Received in revised form 5 February 2010 Accepted 5 February 2010 Available online 19 March 2010 Keywords: Microchannel heat sinks Electronic cooling Wavy microchannels Chaotic advection Dean vortices Dynamical system Poincare section abstract Laminar liquid–water flow and heat transfer in three-dimensional wavy microchannels with rectangular cross section are studied by numerical simulation. The flow field is investigated and the dynamical sys- tem technique (Poincaré section) is employed to analyze the fluid mixing. The results show that when liquid coolant flows through the wavy microchannels, secondary flow (Dean vortices) can be generated. It is found that the quantity and the location of the vortices may change along the flow direction, leading to chaotic advection, which can greatly enhance the convective fluid mixing, and thus the heat transfer performance of the present wavy microchannels is much better than that of straight microchannels with the same cross section. At the same time, the pressure drop penalty of the present wavy microchannels can be much smaller than the heat transfer enhancement. Furthermore, the relative wavy amplitude of the microchannels along the flow direction may be varied for various practical purposes, without com- promising the compactness and efficiency of the wavy microchannels. The relative waviness can be increased along the flow direction, which results in higher heat transfer performance and renders the temperature of the devices much more uniform. The relative waviness can also be designed to be higher at high heat flux regions for hot spot mitigation purposes. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Due to rapid increase in power density and miniaturization of electronic packages, traditional cooling approaches using fans or metal fins may be impractical or unable to meet the ever-increas- ing cooling demands of emerging electronic devices. The thermal issue is now a critical bottleneck for further development of ad- vanced electronic products. According to the International Tech- nology Roadmap for Semiconductors (ITRS), the peak power consumption of high-performance desktops will rise by 96% (147 W–288 W) in 2016, and by 95% (91 W–158 W) in lower-end desktops in 2016 [1]. If no action is taken to develop more effective and innovative cooling methods, die temperatures will inevitably escalate, culminating in reduced mean-time-to-failure and perfor- mance degradation. One promising solution to the problem is direct liquid cooling incorporating microchannels [2–8]. Relevant studies include sin- gle-phase cooling and two-phase (boiling) cooling. While the latter has a potentially higher heat removal capacity, it involves complex issues such as saturation temperature, condensation, nucleation site activation, critical heat flux etc. For intermediate heat fluxes, single-phase cooling offers an alternative that is simpler to imple- ment and is thus preferable [5]. With regard to single-phase cool- ing, due to the reduced feature size of microchannels and the increased influence of surface tension, high flow rates (or equiva- lently, high Reynolds numbers) will cause a sharp increase in pres- sure loss and hence pumping power. The coolant flow through microchannels is invariably laminar, and turbulent convective heat transfer, which is a more efficient mode of heat transfer, is not viable. The use of microchannel cooling for extremely high power den- sity electronic cooling applications was first described in the clas- sical paper by Tuckerman and Pease [2]. Their work sparked off tremendous research interests in the application of microchannel based heat sinks for electronic cooling. A conventional microchan- nel heat sink generally employs straight channels in which the streamlines of the coolant are nearly straight. The resultant fluid mixing is poor and the heat transfer is inefficient. Furthermore, sig- nificant temperature variations across the chip can persist since the heat transfer performance deteriorates in the flow direction in conventionally straight microchannels, as the boundary layers thicken. Moreover, the heat flux in a chip may be not uniform, thus resulting in hot regions which are not easy to remove using con- ventional microchannel heat sinks. These in turn will compromise the reliability of the ICs and can lead to early failures. It is therefore highly desirable to further enhance the heat transfer performance of microchannel heat sinks, without the cost of large pumping power or inducing complicated three-dimensional structures in the microchannel which would make the fabrication difficult. It has been well-known that when liquid flows through curved passages, secondary flows (Dean vortices) may be generated, 0017-9310/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijheatmasstransfer.2010.02.022 * Corresponding author. Tel.: +65 6516 8037. E-mail address: mpeteocj@nus.edu.sg (C.J. Teo). International Journal of Heat and Mass Transfer 53 (2010) 2760–2772 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt